Ball Bank - Comfort is not everything.

A ball bank is an instrument to measure and signpost a comfortable speed for negotiating bends. A car is driven several times around the bend. A reading is taken from the ball bank and a sign is then posted to indicate an advisory speed for this corner.

In the previous article I queried why the visibility around the bend is not taken into consideration. I assumed that a blind bend has to be taken at a slower pace than an open corner.

When giving instructions on cornering I tell my student to firstly position the vehicle for maximum visibility. They never must assume it is clear around a bend. Speed must be reduced to the point where they are able to stop in time should an obstruction block their way around the blind bend (or crest of hill). It should follow the basic rule

Total stopping distance = Reaction time + Braking distance.

The Seeing distance must not be smaller than the Total Stopping distance.

I know of one slight bend on a downhill stretch of narrow road that is totally blind. The advisory sign reads 65 km/h (40 mph) which I regard far too fast for this blind bend. Yes, driver and passenger may feel comfortable at this speed, but with limited vision and downhill, 50 km/h is a more appropriate speed.

A bend should not be sign-posted according to what feels comfortable, but must show the speed at which a vehicle can turn and still stop safely should something block the path around the bend. Motor bikes are especially prone to crashing on winding roads, because riders can enter a bend much faster than a car. 

Crashes involving motor cyclists are of a much higher proportion than that of cars. Could this be because motor cyclists don’t take into consideration the seeing factor when negotiating bends?

For blind bends the seeing factor should over rule the comfortable speed reading by the ball bank.

Index